Device for measuring and monitoring gas flowrates

ABSTRACT

An apparatus for measuring the fluid flowrate through a system whose through flowrate is to be measured, which includes a first chamber in fluid communication and substantial pressure equilibrium with a constant pressure source, a second chamber in fluid communication with the constant pressure source through a flow restrictor whose through flowrate is substantially equal to the through flowrate of the system to be measured, a valve having an upstream port in fluid communication with the second chamber and a downstream port adapted to receive and connect with the system to be measured, the valve being selectively actuable to establish or block fluid communication between the second chamber and the system to be measured, and a measuring device for measuring the pressure difference between the first and second chambers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements made to gas flowratemeasuring and monitoring devices, in particular devices with lowflowrates.

2. Description of the Prior Art

Certain known devices use the deformation of two deformable chamberssupplied with the same gas pressure higher than atmospheric pressure, tomeasure and monitor the gas flowrate.

In these devices, one of the chambers is supplied with said gas pressurethrough a flowrate restriction device, the flowrate of which issubstantially the same order of magnitude as that to be measured.Moreover, this chamber can be placed in communication with the ambientatmosphere and hence with atmospheric pressure when the device is in theresting position, and in communication with the system of which theflowrate is to be measured, when the device is in the measuringposition.

In the resting position, the pressure prevailing in the first chamber isthe supply pressure, and the pressure in the second chamber is close toatmospheric pressure.

In the measuring position, the pressure prevailing in the first chamberremains equal to the supply pressure, and the pressure in the secondchamber increases up to a value slightly less than the supply pressure;the difference in pressure results from the pressure loss experienced bythe gas flow as it passes through the system whose flowrate is to bemeasured and hence depends on the flowrate of the latter.

Thus, it is the difference in pressure between the two chambers thatenables the flowrate to be monitored to be measured and, for thispurpose, deformation of these chambers is detected, which deformationcan be amplified in any fashion--mechanically, electronically, orotherwise.

The drawback of this type of device resides in the fact that it has arelatively long response time, which is inherent in its very design,since the pressurized gas passes into the second chamber at the time ofmeasurement through the flowrate restriction device. If a more precisemeasurement were to be made, the flowrate of the restriction devicewould have to be decreased by comparison with the flowrate to bemeasured, which would extend the response time even longer, while to cutdown the response time a restriction device with a higher flowrate thanthe flowrate to be measured would have to be provided, in which casemeasurement would be less accurate.

SUMMARY OF THE INVENTION

The purpose of the present invention is to supply a device for measuringand monitoring low gas flowrates which has both a short response timeand high sensitivity.

The device according to the invention has two deformable chambers, thefirst being solely and permanently in direct communication with apressure source and the second being, on the one hand, permanently incommunication with a source at the same pressure through a flowraterestriction device whose flowrate is substantially the same as theflowrate desired for the system to be monitored and, on the other hand,when the device is in the measuring position, in communication with theatmosphere through the system to be monitored, characterized by a valvebeing disposed on the gas path between the second chamber and the systemto be monitored, said valve being closed when the device is in theresting position and open when the device is in the measuring ormonitoring position.

The first advantage of such a device is the decrease in response timedue essentially to the small differential between the resting and themeasuring pressures. Because of this small differential, only a smallvolume of gas need be passed through the flowrate restriction device forthe device to be set in the measuring configuration.

A second advantage, derived from the first, is that, because of itsrapid response, a device according to the invention can be usedcontinuously to monitor an adjustment operation while it is in process,as will be explained hereinbelow.

Other advantages will appear in the course of the descriptionhereinbelow with regard to the attached drawings which provide, forindicative and not limitative purposes, some embodiments of theinvention, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show schematically the application of the invention to theflowrate-measuring process in the resting position and measuringposition, respectively.

FIGS. 3 and 4 give two variant applications of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1 and 2, the device has two chambers 1 and 2 separated by adeformable membrane 3.

Chamber 1 is connected directly by a tube 4 to a pressure source P, notshown, at higher than atmospheric pressure.

Chamber 2 is connected to the same pressure source P by means of abranch line 5 and a restriction device 6. It also has an outgoing line 7connected by means of valve 8 to a system 9 to be monitored.

In the resting position (FIG. 1) valve 8 is closed such that thepressure is identical to that inside chambers 1 and 2 and equal tosource pressure P. As a result, membrane 3 is no longer deformed.

When valve 8 is open (FIG. 2) chamber 2 is placed in communication withthe atmosphere via system 9 to be monitored and, hence, there is apressure drop in this chamber. This chamber is always in communicationwith pressure source P, but because of the pressure loss caused byflowrate restriction device 6, the pressure remains less than P. It isprecisely the pressure differential between chambers 1 and 2 whichenables the flowrate of system 9 to be measured.

This pressure differential causes membrane 3 to deform, whichdeformation can be amplified and converted to a measurement of the gasflowrate inside system 9 to be monitored, by classical means, forexample mechanical, electronic, or other, not shown.

Since, in each chamber, the pressures are the same at rest and when themeasuring configuration is initiated, the response time is obviouslydecreased by comparison with known devices wherein chamber 2 must passfrom atmospheric pressure, which is its pressure in the resting state,to the pressure of the other chamber in order for the measuringoperation to be able to take place.

In order further to decrease the response time of the device, theapplicant has designed and developed the valve illustrated in FIG. 3.

This valve, designated by general reference number 11, essentiallycomprises a body 12, a poppet 14, a plug 20, and a spring 18.

At its lower part, body 12 has a cavity 13 at the bottom of which isaccommodated an O-ring 15. The upper part of body 11 comprises a secondcylindrical cavity 17 communicating with cavity 13 by a passage 19wherein poppet 14 is accommodated. The latter is forced against thebottom 16 of cavity 17 via spring 18 which rests on a plug 20, screwedinto the upper part of said cavity 17.

The lower part of poppet 14 is provided with a guide 22 which passesthrough passage 19 and emerges in lower cavity 13.

Cavity 17 communicates with the second chamber 2 of the measuring deviceby a line 23 connected to a tubulature 21 which is made integral withplug 20.

The assembly 26 of which the flowrate is to be measured is composed of abell 25 whose bottom is pierced by a passage 27 and inside which isplaced a washer 29 made of a permeable, compressible material. Thiswasher is crushed against the bottom of said bell by a stopper 31provided with longitudinal flutes 33 on its periphery and a central pin35.

The assembly formed by the device of FIG. 1 and the valve of FIG. 3functions as follows:

Initially poppet 14 is forced against its seat 16 such that chamber 2 ofthe measuring device of FIG. 1 is pressurized. Assembly 26 is thenintroduced into cavity 13 and placed against the bottom of this cavity.During this placement operation, pin 35 forces back guide 22 and raisespoppet 14, placing chamber 2 in communication with the atmospherethrough permeable compressible washer 29, passage 19, cavity 17,tubulature 21, and line 23.

As has already been explained, a pressure drop occurs in chamber 2,resulting in deformation of membrane 3, and measuring this deformationreveals the flowrate of system 26.

It should be noted that pin 35 and guide 22, by their presence inpassages 19 and 27, contribute to decreasing the dead volume existingbetween the blocking means composed of poppet 14, O-ring 15, and washer29.

FIG. 4 shows another embodiment of the valve according to the inventionwhich not only enables the flowrate to be measured by means of apermeable washer in a given state of compression, but also enables theoperation of adjusting the compression status of the permeable washeruntil the desired flowrate is obtained, to be continuously monitored.This case occurs in particular when it is desired to adjust the flowrateof a liquefied-gas lighter expansion valve.

This expansion valve, designated by general reference 61, is composed ofa cylindrical jacket 60 with internal threads, having several lengthwisegrooves 71. Inside said envelope are disposed successively acompressible, permeable pellet 66, a metal washer 64, and a compressingdevice 62, provided with a slot 69, which screws into cylindrical jacket60.

To adjust such an expansion valve, compressing device 62 is screwed downmore or less using slot 69, causing compressible permeable pellet 66 tobe crushed between metal washer 64 and the bottom of cylindrical jacket60.

The gas passing through grooves 71 arrives at compressible permeablepellet 66, through whose compressed part it must pass. The central partof the pellet could be used, by means of the wide orifice 70 provided inthe bottom of cylindrical jacket 60, to bring about a second adjustmentbeyond the limit imposed by the compressed part of the pellet.

The device used to adjust expansion valve 61 is composed of acylindrical body 50 having the following, arranged sequentially: at itsupper part, an accommodation receiving a poppet 55 provided at its endwith a seal 57; at its middle, a chamber 56 connected by a passage 58 tochamber 2 in FIGS. 1 and 2, and a passage 54; and, at its lower part, acavity 52.

For adjustment purposes, the latter receives expansion valve 61 whoseperiphery is isolated from passage 54 by an O-ring 68.

The device according to FIG. 4 operates as follows:

Before the measuring operation, chamber 56 is at the same pressure P aschamber 2 in FIG. 1.

When poppet 55 is lifted by some means not part of the presentinvention, chamber 56 is placed in communication with the atmospherethrough compressible, permeable pellet 66 and through grooves 71 andhence the pressure in chamber 2 drops. If this pressure drop does notcorrespond to the desired flowrate, it can be varied by screwing orunscrewing compressing device 62. In the case, for example, where thepressure drop is too severe, compressing device 62 is screwed down and,because of the gas arriving in chamber 2 from the pressure source, thepressure rises in this chamber as compresing device 62 is screwed down.

When the desired value is reached, screwing is stopped and the expansionvalve can be removed from the device according to the invention.

Obviously, it is the reaction speed of the device according to theinvention which enables it to be used to monitor and adjustmentoperation while the latter is in progress.

While the invention has been illustrated by way of a description of apreferred embodiment, substitutions of various equivalents can beeffected which do not depart from the spirit or scope of the inventionas set forth in the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:
 1. Apparatus for measuring the flowrate of a fluid through a system whose through flowrate is to be measured, comprising:a first chamber in fluid communication and substantial pressure equilibrium with a substantially constant pressure source; a second chamber in fluid communication with said constant pressure source through a flow restrictor having a through flowrate substantially equal to the through flowrate of the system to be measured; a valve having an upstream port and a downstream port, said upstream port being in fluid communication with said second chamber and said downstream port being adapted to receive and connect with the system to be measured, said valve being selectively actuable between a first state wherein fluid communication between said second chamber and the system to be measured is blocked and a second state wherein fluid communication between said second chamber and the system to be measured is established; means for actuating said valve from said first state to said second state upon connection of the sysstem to be measured to said valve and for actuaing said valve from said second state to said first state upon disconnection of the system to be measured from said valve; and pressure difference measuring means for measuring the pressure difference between said first and second chambers.
 2. The apparatus of claim 1, wherein said valve includes a passageway connecting said second chamber and the system to be measured when said system is connected to said valve, and further comprising blocking means for blocking fluid communication through said passageway, at least a portion of said blocking means being disposed within said passageway.
 3. The apparatus of claim 2, wherein said blocking means comprises a poppet valve member and said portion comprises a stem of said poppet valve member.
 4. The apparatus of claim 3, wherein said first and second chambers have a common deformable wall and wherein said pressure difference measuring means comprises means for detecting a deformation of said wall. 